Cache-Timing Attack Against HQC

In this paper, we present the first chosen-ciphertext (CC) cache-timing attacks on reference implementation of HQC. We build a based distinguisher for implementing plaintext-checking (PC) oracle. The PC oracle uses side-channel information to check if given ciphertext decrypts message. This is done by identifying vulnerability during generating process two vectors in also propose new method using oracles against HQC, which may have independent interest.We show general proof-of-concept attack, where use Flush+Reload technique and derive, more detail, practical attack an HQC execution Intel SGX, Prime+Probe used. exact path do key recovery explaining detailed steps, both scenarios, requires 53, 857 traces average with much fewer calls than timing Guo et al. CHES 2022 implementation.